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PRINTING MOTION PICTURE FILM 1 45
'M', the hold-back sprockets *N\ the supply spools *P' and the take-up spools 'Q\
An optical step printer has advantages over the contact machine previously described and has a wider field of application. Many occasions arise when it is desirable to 'stretch' an original negative, that is, assuming an old, silent negative, is required to be printed into a sound film such a state of affairs often arises when old famous scenes are required for a modern historical film it will be necessary to run the final print at 24 frames per second, in order to maintain correct sound reproduction. However, the original old negative was almost certainly 'shot' at 16 or less frames per second. If the speed of the original is merely increased the action will appear too fast. It is therefore necessary to so gear the printer that 24 pictures are moved through the positive head every time 16 pictures are moved through the negative head. This is done by printing two copies of every other frame throughout the negative film. Obviously, such an adjustment would be impossible with a contact printer.
Travelling Matts
The introduction of transitional effects may also be made on this type of printer, although it is more convenient to use a more elaborate machine. Let us assume that a very simple transition is to be made whereby a thin line passes across the screen, wiping the first scene away and revealing the second scene in its wake. This effect, known as the 'Horizontal Wipe', may be made on the Optical Step Printer just described by either of two methods, firstly by using the 'Travelling Matt' and, secondly, by using an auxiliary mask. The principle of the Travelling Matt is best understood by reference to Figure 62. For simplicity the six film strips shown in this figure are represented by series of rectangles, indicating the frames, and the perforations and film edges have been omitted. The strip of film shown at 'A' and carrying the title 'PICTURE' is required to 'wipe' to the second title carrying the word 'SOUND', and shown at 'D'. When the negative of 'A' is in the printer a strip of film partially opaque, as shown at 'B', is threaded in contact with the positive film and facing the negative. After the film has been printed this film strip 'B' will have cut off parts of each picture and only have printed those sections shown at 'C. The positive film is then rewound to the position at which the first film strip, or matt, started but this time the matt shown at 'E' is threaded in contact with the positive film. Negative 'D' is then placed in the printer and, since matt 'E' will protect those
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